One of the tasks of the World Health Organization (WHO) is the development of environmental health criteria. In this connection, it has been concerned with some problems related to the concept of indicator bacteria and the rapid and reliable identification of pathogenic ones. WHO requires the absence of any organisms of fecal origin in drinking water and refers to Escherichia coli, fecal streptococci, and Clostridium perfringens as the most representative of fecal pollution. Potable water supplies for aviation and shipping have to be of similar quality. To assist in the control of surface water pollution, a manual, which includes a chapter on bacteriological examination, has been prepared to encourage the use of approved analytical methods. Attention has also been given to the survey and examination of recreational and shellfish-bed waters.